Silicene has introduced itself as an outstanding novel material, which seeks its meritorious place among common spintronic devices like Cu and Ag. In this work, photogalvanic effect in silicene is studied within the semi-classical approach and beyond Dirac point approximation. Normal electric field plays the role of effective pseudo-magnetic field which breaks the inversion symmetry and splits the conduction and valence bands. The interplay between this external field and intrinsic spin-orbit coupling provides spin-valley locking in silicene. Spin-valley locking in silicene makes this material superior to its carbon counterpart, graphene. Since the absorption of the polarized photons is not equivalent at both of the valleys, spin-valley locking leads to a spin-polarized photocurrent injection.
We study the circular photogalvanic effect in the organometal halide perovskite solar cell absorber CH$_3$NH$_3$PbI$_3$. For crystal structures which lack inversion symmetry, the calculated photocurrent density is about $10^{-9}$ A/W, comparable to the previously studied quantum well and bulk Rashba systems. Because of the dependence of the circular photogalvanic effect on inversion symmetry breaking, the degree of inversion asymmetry at different depths from the surface can be probed by tuning the photon energy and associated penetration depth. We propose that measurements of this effect may …
Spin photogalvanic effect (SPGE) is an efficient method to generate a spin current by photoexcitation in a contactless and ultra-fast way. In two-dimensional (2D) collinear antiferromagnetic (AFM) materials that preserve the combined time-reversal (T) and inversion (I) symmetry (i.e., TI symmetry), we find that the photogalvanic currents in two magnetic sublattices carry different kinds of spins and propagate in opposite direction if the spin-orbit coupling is negligible, resulting in a pure spin current without net charge current. Based on the first-principles calculations, we show that two e…
Silicene, as the silicon analog of graphene, has been successfully fabricated by epitaxial growing on various substrates. Similar to free-standing graphene, free-standing silicene possesses a honeycomb structure and Dirac-cone-shaped energy band, resulting in many fascinating properties such as high carrier mobility, quantum spin Hall effect, quantum anomalous Hall effect, and quantum valley Hall effect. The maintenance of the honeycomb crystal structure and the Dirac cone of silicene is crucial for observation of its intrinsic properties. In this review, we systematically discuss the substrat…
We report on the observation of the magneto-photogalvanic effect (MPGE) due to inter-subband transitions in (001)-oriented GaAs quantum wells. This effect is related to the gyrotropic properties of the structures. It is shown that inter-subband absorption of linearly polarized radiation may lead to spin-related as well as spin independent photocurrents if an external magnetic field is applied in the plane of the quantum well. The experimental results are analyzed in terms of the phenomenological theory and microscopic models of MPGE based on either asymmetric optical excitation or asymmetric r…
The electronic structure of the recently synthesised (3x3) reconstructed silicene on (4x4) Ag(111) is investigated by first-principles calculations. New states emerge due to the strong hybridization between silicene and Ag. Analyzing the nature and composition of these hybridized states, we show that i) it is possible to clearly distinguish them from states coming from the Dirac cone of free-standing silicene or from the sp-bands of bulk Ag and ii) assign their contribution to the description of the linearly dispersing band observed in photoemission. Furthermore, we show that silicene atoms co…
By using first-principles calculations, the electronic structure of planar and strained in-plane graphene/silicene heterostructure is studied. The heterostructure is found to be metallic in a strain range from -7% (compression) to +7% (tension). The effect of compressive/tensile strain on the chemical activity of the in-plane graphene/silicene heterostructure is examined by studying its interaction with the H2O molecule. It shows that compressive/tensile strain is able to increase the binding energy of H2O compared with the adsorption on a planar surface, and the charge transfer between the wa…
The circular photogalvanic effect (CPGE) has been observed in (100)-oriented $p$-GaAs/AlGaAs quantum wells at normal incidence of far-infrared radiation. It is shown that monopolar optical spin orientation of free carriers causes an electric current which reverses its direction upon changing from left to right circularly polarized radiation. CPGE at normal incidence and the occurence of the linear photogalvanic effect indicate a reduced point symmetry of studied multi-layered heterostructures. As proposed, CPGE can be utilized to investigate separately spin polarization of electrons and holes …
The circular photogalvanic effect (CPGE) is the only possible quantized signal in Chiral Weyl and multi-fold semimetals with inversion and mirror symmetries broken. Here, we review CPGE in the chiral multifold semimetals in terms of classification of CPGE tensor, the quantization of CPGE from k.p effective model and topological semimetal RhSi family. Firstly, we give complete symmetric analysis of CPGE tensors for all nonmagnetic point groups, and get a table classifying matrix of response tensors. Secondly, the CPGE becomes a quantized response in the noncentrosymmetric topological semimetals…
We investigate the effect of lattice disorder and local correlation effects in finite and periodic silicene structures caused by carbon doping using first-principles calculations. For both finite and periodic silicene structures, the electronic properties carbon-doped monolayers are dramatically changed by controlling the doping sites in the structures, which is related to the amount of disorder introduced in the lattice and electron-electron correlation effects. By changing the position of the carbon dopants, we found that a Mott-Anderson transition is achieved. Moreover, the band gap is dete…
We show theoretically that electromagnetic waves propagating in the transparency region of a non-centrosymmetric medium can induce a dc electric current. The origin of the effect is the Raman scattering of light by free carriers in the system. Due to the photon scattering, electrons undergo real quantum transitions resulting in the formation of their anisotropic momentum distribution and in shifts of electronic wavepackets giving rise to a steady state photocurrent. We present microscopic theory of the Raman Photogalvanic effect (RPGE) focusing on two specific situations: (i) generic case of a…
Tin sulfide promises very interesting properties such as a high optical absorption coefficient and a small band gap, while being less toxic compared to other metal chalcogenides. However, the limitations in growing atomically thin structures of tin sulfide hinder the experimental realization of these properties. Due to the flexibility of the colloidal synthesis, it is possible to synthesize very thin and at the same time large nanosheets. Electrical transport measurements show that these nanosheets can function as field-effect transistors with high on/off ratio and p-type behavior. The tempera…
We introduce the magnon circular photogalvanic effect enabled by stimulated Raman scattering. This provides an all-optical pathway to the generation of directed magnon currents with circularly polarized light in honeycomb antiferromagnetic insulators. The effect is the leading order contribution to magnon photocurrent generation via optical fields. Control of the magnon current by the polarization and angle of incidence of the laser is demonstrated. Experimental detection by sizeable inverse spin Hall voltages in platinum contacts is proposed.
It is shown that the free-carrier (Drude) absorption of circularly polarized radiation in quantum well structures leads to an electric current flow. The photocurrent reverses its direction upon switching the light helicity. A pure orbital mechanism of such a circular photogalvanic effect is proposed that is based on interference of different pathways contributing to the light absorption. Calculation shows that the magnitude of the helicity dependent photocurrent in $n$-doped quantum well structures corresponds to recent experimental observations.
We present a first-principles study of effects of small biaxial strain ($|\varepsilon|\le 5\%$) and perpendicular electric field (E-field) on the electronic and phonon properties of low-buckled silicene and germanene. With an increase of the biaxial strain, the conduction bands at the high symmetric $Γ$ and $M$ points of the first Brillouin zone shift significantly towards the Fermi level in both silicene and germanene. In contrast, the E-field changes the band dispersions near the $Γ$ and open a small band gap at the K point in silicene. We found that the field-induced gap opening in silicene…
We achieve the enhancement of circular photogalvanic effect arising from the photo-injection of spins in topological insulator thin films by tuning the Fermi level ($E_{\rm F}$). A series of (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ thin films were tailored so that the Fermi energy ranges above 0.34 eV to below 0.29 eV of the Dirac point, i.e., from the bulk conduction band bottom to the valence band top through the bulk in-gap surface-Dirac cone. The circular photogalvanic current, indicating a flow of spin-polarized surface-Dirac electrons, shows a pronounced peak when the $E_{\rm F}$ is set near the Dir…
This concise book offers an essential introduction and reference guide for the many newcomers to the field of physics of elemental 2D materials. Silicene and related materials are currently among the most actively studied materials, especially following the first experimental synthesis on substrates in 2012. Accordingly, this primer introduces and reviews the most crucial developments regarding silicene from both theoretical and experimental perspectives. At the same time the reader is guided through the extensive body of relevant foundational literature. The text starts with a brief history o…
Electron spin resonance driven photogalvanic effect in graphene-based structures
Université de Montpellier, CNRS（蒙彼利埃大学，法国国家科学研究中心）；Institute of Experimental and Applied Physics, University of Regensburg（雷根斯堡大学实验与应用物理研究所）；CENTERA Labs, Institute of High Pressure Physics, PAS（波兰科学院高压物理研究所 CENTERA 实验室）；Institute of Theoretical Physics and Halle-Berlin-Regensburg Cluster of Excellence CCE, University of Regensburg（雷根斯堡大学理论物理学院及哈雷-柏林-雷根斯堡卓越集群 CCE）；Institute of Physical Chemistry, Friedrich Schiller University Jena（耶拿弗里德里希·席勒大学物理化学研究所）；Institute of High Pressure Physics of the Polish Academy of Sciences（波兰科学院高压物理研究所）；Research Center for Electronic and Optical Materials, National Institute for Materials Science（物质材料研究机构电子与光学材料研究中心）
We report a hierarchical first-principles investigation on the entangled effects of lattice dimensionality and bond characteristics in the lattice dynamics of silicene and germanene. It is found that bond bending (stretching) negatively (positively) contributes to Grüneisen constant, which results in the negative acoustic (positive optical) Grüneisen constant. The layer thickening (bond weakening) caused by chemical functionalization tends to increase (decrease) the acoustic (optical) Grüneisen constant, due to the increased (decreased) bond-stretching effect. The excitation of the negative-$γ…
Structural and electronic properties of the all-Si analogue of graphene, silicene have elucidated through DFT calculations. Silicene differs considerably from graphene in being `chair-type' puckered in each 6-membered ring which leads to ordered ripples across the surface. Binding energies suggest stability for such rippled silicenes and are predicted to behave as a finite gap semi-conductor with electron-hole symmetry quenched. Inter-layer coupling between the silicenes is suggested as the mechanism for the formation of the bulk-Si in its only known diamond form.
The stability and electronic structure of competing silicene phases under in-plane compressive stress, either free-standing or on the ZrB$_2$(0001) surface, has been studied by first-principles calculations. A particular ($\sqrt{3}\times\sqrt{3}$)-reconstructed structural modification was found to be stable on the ZrB$_2$(0001) surface under epitaxial conditions. In contrast to the planar and buckled forms of free-standing silicene, in this "planar-like" phase, all but one of the Si atoms per hexagon reside in a single plane. While without substrate, for a wide range of strain, this phase is e…
Long carrier lifetimes and diffusion lengths form the basis for the successful application of the organic-inorganic perovskite (CH$_3$NH$_3$)PbI$_3$ in solar cells and lasers. The mechanism behind the long carrier lifetimes is still not completely understood. Spin-split bands and a resulting indirect band gap have been proposed by theory. Using near band-gap left-handed and right-handed circularly polarized light we induce photocurrents of opposite directions in a single-crystal (CH$_3$NH$_3$)PbI$_3$ device at low temperature ($4~\mathrm{K}$). The phenomenom is known as the circular photogalva…
We investigate the generation and temperature-induced evolution of optically-driven spin photocurrents in WTe$_2$ and MoTe$_2$. By correlating the scattering-plane dependence of the spin photocurrents with the symmetry analysis, we find that a sizeable spin photocurrent can be controllably driven along the chain direction by optically exciting the system in the high-symmetry $y$-$z$ plane. Temperature dependence measurements show that pronounced variations in the spin photocurrent emerge at temperatures that coincide with the onset of anomalies in their transport and optical properties. The de…
The deposition of one silicon monolayer on the silver (111) substrate in the temperature range 150-300$^\circ$C, gives rise to a mix of (4$\times$4), ($2\sqrt{3}\times 2\sqrt{3}$)R30$^\circ$ and ($\sqrt{13}\times\sqrt{13}$)R13.9$^\circ$ superstructures which strongly depends on the substrate temperature. We deduced from a detailed analysis of the LEED patterns and the STM images that all these superstructures are given by a quasi identical silicon single layer with a honeycomb structure (i.e. a silicene-like layer) with different rotations relatively to the silver substrate. The STM images mor…
The paper overviews experimental and theoretical studies of photogalvanic effects induced in BiSbTe- based three dimensional topological insulators by polarized terahertz radiation. We present the state-of-the-art of this subject, including most recent and well-established results. We discuss a phenomenological theory based on symmetry arguments and models illustrating the photocurrents origin. We give a brief glimpse of the underlying microscopic theory, as well as an overview of the main experimental results.
By applying density functional theory calculations, we predict that the groundstate of bilayer silicene at certain interlayer distances can be antiferromagnetic. At small electron or hole doping, it becomes half metallic under applied out-of-plane electric field, which can be used to produce fully spin-polarized field-effect-driven current even in the absence of external magnetic field, ferromagnetic substrates, doped magnetic ions, or spin-orbital coupling. Our finding points out a new route to overcome the major challenge of spintronics.
Utilizing spin or valley degree of freedom is one of the promising approaches to realize more energy-efficient information processing. In the 2D transition metal dichalcogenide, the spin/valley current can be generated by utilizing the circular photogalvanic effect (CPGE), i.e., the generation of photocurrent by a circularly polarized light. Here we show that an in-plane electric field at MoS2/WSe2 heterostructure-electrode boundary results in an electrically tunable circular photogalvanic effect (CPGE) under optical excitation with normal incidence. The observed CPGE can be explained by the v…
We engineer quantum anomalous Hall effect in silicene via doping 3d transition metals. We show that there exists a stable quantum anomalous Hall effect in Vanadium doped silicene using both analytical model and Wannier interpolation. We also predict the quantum valley Hall effect and electrically tunable topological states could be realized in certain transition metal doped silicene where the energy band inversion occurs. Our finding provides new scheme for the realization of quantum anomalous Hall effect and platform for electrically controllable topological states.
Weyl semimetals are gapless topological states of matter with broken inversion and/or time reversal symmetry, which can support unconventional responses to externally applied electrical, optical and magnetic fields. Here we report a new photogalvanic effect in type-II WSMs, MoTe2 and Mo0.9W0.1Te2, which are observed to support a circulating photocurrent when illuminated by circularly polarized light at normal incidence. This effect occurs exclusively in the inversion broken phase, where crucially we find that it is associated with a spatially varying beam profile via a new dispersive contribut…
Silicene (a monolayer of silicon atoms) is a quantum spin-Hall insulator, which undergoes a topological phase transition into other insulators by applying external field such as electric field, photo-irradiation and antiferromagnetic order. We investigate the electronic and transport properties of silicene nanoribbons based on the Landauer formalism. We propose to determine topological phase transitions by measuring the density of states and conductance. The conductance is quantized and changes its value when the system transforms into different phases. We show that a silicene nanoribbon near …
Epitaxial silicene, which is one single layer of silicon atoms packed in a honeycomb structure, demonstrates a strong interaction with the substrate that dramatically affects its electronic structure. The role of electronic coupling in the chemical reactivity between the silicene and the substrate is still unclear so far, which is of great importance for functionalization of silicene layers. Here, we report the reconstructions and hybridized electronic structures of epitaxial 4x4 silicene on Ag(111), which are revealed by scanning tunneling microscopy and angle-resolved photoemission spectrosc…
Observation and Control of the Magnetic Photogalvanic Effect from Strongly Bound Excitons
Institute for Quantum Computing, University of Waterloo（滑铁卢大学量子计算研究所）；Department of Physics and Astronomy, University of Waterloo（滑铁卢大学物理与天文学系）；Department of Electrical and Computer Engineering, University of Waterloo（滑铁卢大学电气与计算机工程系）；Department of Physics, National University of Singapore（新加坡国立大学物理系）；Department of Physics, University of Michigan（密歇根大学物理系）；Department of Chemistry, University of Waterloo（滑铁卢大学化学系）；School of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials & Micro-nano Devices, Renmin University of China（中国人民大学物理学院及光电功能材料与微纳器件北京市重点实验室）；Key Laboratory of Quantum State Construction and Manipulation (Ministry of Education), Renmin University of China（中国人民大学量子态构建与操控教育部重点实验室）
We develop a theory of circular photogalvanic effect (CPGE) for classically high photon energies which exceed the electron scattering rate but are small compared to the average electron kinetic energy. In this frequency range one can calculate the CPGE by using two different approaches. In the fully quantum-mechanical approach we find the photocurrent density by applying Fermi's golden rule for indirect intraband optical transitions with virtual intermediate states both in the conduction and valence bands. In the framework of the semiclassical approach, we apply a generalized Boltzmann equatio…
We show that an electrical shift current is generated when electrons are photoexcited from the valence to conduction bands on a BN nanotube. This photocurrent follows the light pulse envelope and its symmetry is controlled by the atomic structure of the nanotube. We find that the shift current has an intrinsic quantum mechanical signature in which the chiral index of the tube determines the direction of the current along the tube axis. We identify discrete lattice effects in the tangent plane of the tube that lead to an azimuthal component of the shift current. The nanotube shift current can l…
Electric and thermoelectric properties of silicene nanoribbons doped with Al and P impurity atoms are investigated theoretically for both antiparallel and parallel orientations of the edge magnetic moments. In the former case, appropriately arranged impurities can lead to a net magnetic moment and thus also to spin thermoelectric effects. In the latter case, in turn, spin thermoelectric effects also occur in the absence of impurities. Numerical results based on ab-initio calculations show that the spin thermopower can be considerably enhanced by the impurities.
We investigate the anomalous effects due to the Berry correction and the considerable perturbations in the silicene-like hexagonal lattice system. The Berry curvature in periodic Bloch band system which related to the electromagnetic field is explored, the induced transverse anomalous velocity gives rise to the intrinsic Hall conductivity (without the vertex correction) expecially in the quantum anomalous Hall phase. The quantum anomalous Hall effect which related to the anomalous velocity term is detected, including the band avoided corssing effect and the generated special band gap. %{Enlarg…
Using density functional theory and non-equilibrium Greens function technique, we performed theoretical investigations on the structural and transport properties of zigzag silicene nanoribbons with Stone-Wales defect. The calculated formation energy is significantly lower than that of graphene and silicene, which implies the high stability of such defect in SiNRs. Negative differential resistance can be observed within certain bias voltage range in both perfect and SW defected SiNRs. In order to elucidate the mechanism the NDR behavior,the transmission spectra and molecular projected self-cons…
We use the tight-binding model and the random-phase approximation to investigate the intrinsic plasmon in silicene. At finite temperatures, an undamped plasmon is generated from the interplay between the intraband and the interband-gap transitions. The extent of the plasmon existence range in terms of momentum and temperature, which is dependent on the size of single-particle-excitation gap, is further tuned by applying a perpendicular electric field. The plasmon becomes damped in the interband-excitation region. A low damped zone is created by the field-induced spin split. The field-dependent…
We investigate quantum Hall effects in silicene by applying electric field $E_z$ parallel to magnetic field. Silicene is a monolayer of silicon atoms forming a two-dimensional honeycomb lattice, and shares almost every remarkable property with graphene. A new feature is its buckled structure, due to which the band structure can be controlled externally by changing $E_z$. The low energy physics of silicene is described by massive Dirac fermions, where the mass is a function of $E_z$ and becomes zero at the critical field $E_{\text{cr}}$. We show that there are no zero energy states due to the D…
Silicene is a monolayer of silicon atoms forming a two-dimensional honeycomb lattice, which shares almost every remarkable property with graphene. The low energy structure of silicene is described by Dirac electrons with relatively large spin-orbit interactions due to its buckled structure. The key observation is that the band structure is controllable by applying the electric field to a silicene sheet. We explore the phase diagram of silicene together with exchange field $M$ and by applying electric field $E_{z}$. There appear quantum anomalous Hall (QAH) insulator, valley polarized metal (VP…
Graphene is a two-dimensional (2D) semimetal with high mobility in charge carriers due to the existence of Dirac points. Silicene is another promising material, with properties analog to graphene. Many silicon (Si) based electronic devices can be integrated via graphene-silicene (Gra/si) hybrid structures. These electronic applications are mostly based on the ability to tune the bandgap via electronic structure deformation that is expected to be achieved by multilayer stacking, applying a transverse external electric field (EF), and altering interfacial distance. In this work, we investigate t…
By using first-principles calculations, we predict that an in-plane homogenous electrical field can induce half-metallicity in hydrogen-terminated zigzag silicene and germanene nanoribbons (ZSiNRs and ZGeNRs). A dual-gated finite ZSiNR device reveals a nearly perfect spin-filter efficiency of up to 99% while a quadruple-gated finite ZSiNR device serves as an effective spin field effect transistor (FET) with an on/off current ratio of over 100 from ab initio quantum transport simulation. This discovery opens up novel prospect of silicene and germanene in spintronics.
Starting from the symmetry aspects and tight-binding method in combination with first-principles calculation, we systematically derive the low-energy effective Hamiltonian involving spin-orbit coupling (SOC) for silicene, which is very general because this Hamiltonian applies to not only the silicene itself but also the low-buckled counterparts of graphene for other group IVA elements Ge and Sn, as well as graphene when the structure returns to the planar geometry. The effective Hamitonian is the analogue to the first graphene quantum spin Hall effect (QSHE) Hamiltonian. Similar to graphene mo…
We show that with the help of spin-orbit coupling, nonlinear light-matter interactions can efficiently couple with spin and valley degrees of freedom. This revealed spin photogalvanic effect can generate the long-time pursued intrinsic pure spin current (PSC) in non-centrosymmetric nonmagnetic insulators. Different from the spin and valley Hall effect, such a photo-driven spin current is universal and can be generated without external bias field. Using first-principles simulation, we study monolayer transition metal dichalcogenides (TMDs) to demonstrate this effect and confirm an enhanced PSC …
Bilayer silicene has richer physical properties than bilayer graphene due to its buckled structure together with its trigonal symmetric structure. The buckled structure arises from a large ionic radius of silicon, and the trigonal symmetry from a particular way of hopping between two silicenes. It is a topologically trivial insulator since it carries a trivial $\mathbb{Z}_{2}$ topological charge. Nevertheless, its physical properties are more akin to those of a topological insulator than those of a band insulator. Indeed, a bilayer silicene nanoribbon has edge modes which are almost gapless an…
The effects of biaxial strain on the impurity-induced magnetism in P-doped graphene (P-graphene) and N-doped silicene (N-silicene) are studied by means of spin-polarized density functional calculations, using the supercell approach. The calculations were performed for three different supercell sizes $4\times 4$, $5\times 5$, and $6\times 6$, in order to simulate three different dopant concentrations 3.1, 2.0 and 1.4 %, respectively. For both systems, the calculated magnetic moment is 1.0 $μ_B$ per impurity atom for the three studied concentrations. From the analysis of the electronic structure…
Nonlinear optical responses of quantum materials have recently undergone dramatic developments to unveil nontrivial geometry and topology. A remarkable example is the quantized longitudinal circular photogalvanic effect (CPGE) associated with the Chern number of Weyl fermions, while the physics of transverse CPGE in Weyl semimetals remains exclusive. Here, we show that the transverse CPGE of Lorentz invariant Weyl fermions is forced to be zero. We find that the transverse photocurrents of Weyl fermions are associated not only with the Chern numbers but also with the degree of Lorentz-symmetry …
We have studied the circular photogalvanic effect (CPGE) in Cu/Bi bilayers. When a circularly polarized light in the visible range is irradiated to the bilayer from an oblique incidence, we find a photocurrent that depends on the helicity of light. Such photocurrent appears in a direction perpendicular to the light plane of incidence but is absent in the parallel configuration. The helicity dependent photocurrent is significantly reduced for a Bi single layer film and the effect is nearly absent for a Cu single layer film. Conventional interpretation of the CPGE suggests the existence of spin-…
Considering finite-temperature screened electron-impurity scattering, we present a kinetic equation approach to investigate transport properties of two-dimensional massive fermions in silicene. We find that the longitudinal conductivity is always nonvanishing when chemical potential lies within the energy gap. This residual conductivity arises from interband correlation and strongly depends on strength of electron-impurity scattering. We also clarify that the electron-impurity interaction makes substantial contributions to the spin- and valley-Hall conductivities, which, however, are almost in…
Considering the interband correlation, we present a generalized multiple-scattering approach of Green's function to investigate the effects of electron-impurity scattering on the density of states in silicene. The reduction of energy gaps in the case of relatively high chemical potential and the transformation of split-off impurity bands into band tails for low chemical potential are found. The dependency of optical conductivity on the impurity concentration is also discussed for frequency within the terahertz regime.
So far, the circular photogalvanic effect (CPGE) is the only possible quantized signal in Weyl semimetals. With inversion and mirror symmetries broken, Weyl and multifold fermions in band structures with opposite chiralities can stay at different energies and generate a net topological charge. Such kind of net topological charge can present as a quantized signal in the circular polarized light induced injection current. According to current theoretical understanding, RhSi and its counterparts are believed to be the most promising candidate for the experimental observation of the quantized CPGE…
